1. Field of the Invention
This invention relates to a power supply and more particularly to a power supply which automatically generates the same output voltage when voltages of substantially different magnitudes are applied to its input. The invention also relates to a power supply having a circuit breaker on its input side which provides reliable protection at a single specified power level as the different voltages are applied to the input of the power supply.
2. Backqround of the Invention
It is known to provide power supplies that can operate from different voltages sources at different times, such as for example from 120 and 220 volts. It is desirable that these power supplies automatically alter their operation to generate essentially the same output voltage as the different input voltages are applied. This capability eliminates the necessity of manual intervention to adjust switches, straps, etc. as the different voltages are applied.
Power supplies which perform this operation automatically are shown in U.S. Pat. Nos. 3,348,132, 3,900,787, 4,415,964, 4,590,546, 4,654,538, and 4,665,323. Although all of these patents disclose power supply circuits which automatically adapt their operation to the receipt of different input voltages, none of these disclose a power supply that is protected by a single circuit breaker on its input side that trips when a single fixed output current is exceeded as the different input voltages are applied. In other words, a circuit breaker should trip at a single fixed output current regardless of the magnitude of the voltage applied to the input of the power supply. Thus, if a power supply has a circuit breaker which trips when the input current exceeds 10 amperes at 110 volts, in order to provide the same protection on the output side for a 220 volt input, the circuit breaker should trip when the input current exceeds 5 amperes.
It is desirable to provide quality equipment with circuit breakers in order to protect both the power supply as well as the load to which the power supply is connected. Although power supplies are available which automatically adapt their operation to input voltages of different magnitudes, the unavailability of circuit breakers on the input side which trip at the same output power level regardless of the input voltage, requires manual operations such as the adjustment of straps, the setting of switches, etc. in order to adapt the operation of the circuit breaker to the reception of the different magnitudes of input voltages. The necessity of this manual intervention is a problem in that it is easy to overlook a change in input voltages and thereby damage expensive components or systems. This risk is substantially increased where the input voltage changes frequently and/or rapidly without advance warning or notification to the operator of equipment.